1. Field of the Invention
This invention presents a method and apparatus for an interactive high-resolution volumetric three-dimensional (3D) display using fast spatial light modulators (SLM), a moving image screen, and a wireless pulsed laser pointer.
2. Description of the Related Art
A Brief Survey of Prior Art on Volumetric 3D Display Techniques
In this section, we provide a brief survey of a number of 3D volumetric display techniques that have been intensively developed recently by several research groups.
Solid State Up-Conversion
A fundamental requirement of a volumetric 3D display system is to have an entire volume filled with materials that can be selectively excited at any desired locations. To achieve this goal, one can have two independently controlled radiation beams that activate a voxel only when they intersect. While electron beams can not be used for such a purpose, laser beams can, provided that a suitable excitable material can be found. A process known as two-photon up-conversion can achieve this objective (U.S. Pat. No. 4,041,476 by Swainson, 1977, U.S. Pat. No. 5,684,621 by Downing, 1997). Briefly, this process uses the energy of two IR photons to pump a material into an excited level from which it can make a visible fluorescent transition to a low level. For this process to be useful as a display medium it must exhibit two photon absorption from two different wavelengths so that a voxel is turned on only at the intersection of two independently scanned laser sources. The materials of choice at the present time are the rare earth metals doped into a glass host known as ZBLAN. ZBLAN is a flurozirconate glass whose chemical name stands for ZrF4—BaF2—LaF3—AlF3—NaF. The two photon up-conversion concept for 3D volumetric display is quite promising, since it requires no moving parts. However, the major difficulties to produce a practically useful 3D display using this approach are its scale-up capability and color capability.
Gas Medium Up-Conversion
Another 3D Display based on the up-conversion concept employs the intersection of two laser beams in an atomic vapor, and subsequent omnidirectional florescence from the intersection point (U.S. Pat. No. 4,881,068, November 1989). Two lasers are directed via mirrors and x-y scanners towards an enclosure containing an appropriate gaseous species (rubidium vapor, for example), where they intersect at 90 degrees. Either laser by itself causes no visible fluorescence. However, where both laser are incident on the same gas atoms, two step excitation results in florescence at the intersecting point. By scanning the intersection point faster enough, a 3D image can be drawn in the vapor. The eye can not see changes faster that about 15 Hz, so that if the image to be displayed is repeatedly drawn faster than this rate, the image will appear to be steady, even though light may be originating from any one point in the volume for only a small fraction of the time.
The advantage of this 3D display concept is its scalability: It can be built in almost any desirable size without significantly increasing the complexity of the system. The technical difficulties in implementing this concept including the requirement of a vacuum chamber, the requirement for maintaining a certain temperature, the limitation on the number of voxels due to the speed of the scanners, and concern for the safety of the eyes of viewers due to the use of laser beams.
Rotating Light Emitting Diodes (LEDs) Array
One of the earliest volumetric 3D displays was designed by Schipper (U.S. Pat. No. 3,097,261, 1963). It consists of a rotating electroluminenscent panel with an embedded high-speed light emitter array. By controlling the timing of the x-y addressing of the light emitter array and the rotation of the panel, 3D images can be formed within the volume swept by the rotating panel. In 1979, Berlin developed an innovative approach to solving the high-bandwidth data transmission problem of this design using an optical link and replaced the light emitters with a high speed LED (Light Emitter Diode) matrix (U.S. Pat. No. 4,160,973 by Berlin, 1979). This system uses a 3D array of LEDs that are rotated to sweep out a 3D volume. The resolution of this volume is a function of the number and density of LEDs mounted on the rotating planar array, the speed of rotation and the rate at which the LEDs can be pulsed.
Cathode Ray Sphere
The Cathode Ray Sphere (CRS) concept was originally developed by Ketchpel in the 1960s (U.S. Pat. No. 3,140,415 by Ketchpel, 1960) and recently implemented by researchers in New Zealand (U.S. Pat. No. 5,703,606 December 1997 Blundell). The voxels are created by addressing a rapidly rotating phosphor-coated target screen in vacuum by electron beams synchronized to the screen's rotation. The view of this rotating multiple planar surface depends on the clarity of the glass enclosure and the translucency of the rotating screen. Another image quality issue is the interaction between the phosphor decay rate and the speed of the rotation of the screen.
Varifocal Mirror and High Speed Monitor
A very clever method of 3D display employs the strategy of forming optical virtual 3D images in space in front of a viewer using a varifocal minor system (U.S. Pat. No. 4,130,832 by Sher, 1978). The varifocal mirror system consists of a vibrating circular mirror along with a high-speed monitor. The monitor is connected to a woofer such that the woofer can be synchronized to the monitor. A flexible, circular mirror is attached to the front of the woofer, and the monitor is pointed toward the mirror. With the vibrations from the woofer, the mirror changes focal length and the different points being displayed on the monitor seem to appear at different physical locations in space, giving the appearance of different depths to different objects in the scene being displayed. Variable mirror based 3D display systems are primarily limited by the size of the mirror and updating rate of images, since this mirror has to vibrate.
Laser Scanning Rotating Helix 3D Display
Extensive attempts have been made by researchers at Texas Instruments (U.S. Pat. Nos. 5,042,909, 5,162,787, etc.) to develop a 3D display device based on laser scanning and a rotating (helical) surface. Lasers scanning 3D displays operate by deflecting a beam of coherent light generated by a laser to a rotating helical surface. Timing modulation of the laser beam controls the height of the light spot that is produced by the laser on the rotating surface. The deflectors include devices such as polygonal mirrors, galvanometers, acousto-optics modulated deflectors, and micro-deformable mirrors. There are several problems with this 3D display mechanism that have prevented it from becoming commercially feasible.
The most serious problem is the limitation on the maximum number of voxels that can be displayed. Due to the nature of sequential (non-parallel) laser scanning, only one spot of light can be displayed at any given moment. All the activated image voxels have to be addressed, one by one, by the scanning of a single laser beam in time-multiplex fashion. The time needed for scanning the laser beam, including holding the laser on a particular voxel position long enough to produce sufficient brightness, poses an upper limit to how many voxels the device can display. To increase the number of voxels, multiple channel lasers and scanners could be used. However, many attempts to increase the spatial resolution have been hampered with high cost and bulky hardware design.
As shown in the previously mentioned patents and techniques, there has been a research and development effort for obtaining a true volumetric 3D display. However, none of them is able to provide high-resolution volumetric 3D images with over one million voxels. Further, none of them is able to provide a dynamic interaction with a true volumetric 3D display.